Diseases caused by pathogenic protozoa are important in both human and animal health. Species of Entamoeba, coccidia, Giardia, and Trichomonas are intestinal disease-causing parasites that are responsible for human morbidity and death, and for considerable economic loss in farm animals such as chickens and cattle (Parasitic Protozoa. 1977. Julius P. Kreier, Ed., Academic Press, NY; In Vitro Cultivation of Protozoan Parasites. 1983. James B. Jensen, Ed., CRC Press, FL). For illustration of the instant invention, we have chosen one such parasite, Giardia lamblia, which is responsible for giardiasis, an intestinal disease in humans (Gillin et al. [1986] Infect. Immun. 53:641-645).
Giardia lamblia is a flagellated protozoan that colonizes the upper small intestine of humans and causes the intestinal disease giardiasis. Giardia is a waterborne parasite that is especially prevalent in children, causing symptoms that include diarrhea, malabsorption, and failure to thrive. Symptoms may persist for years or may disappear spontaneously. The disease is both endemic and epidemic in the United States and is often acquired by campers who have drunk from wilderness streams or ponds (Wolfe, M. S. [1978] N. Engl. J. Med. 298:319-321). Travelers outside the United States, especially in underdeveloped countries, may acquire the disease by drinking local, untreated water.
In the upper small intestine, Giardia trophozoites are exposed to complex and highly variable mixtures of food and digestive agents, including enzymes and bile surfactants. It is in this environment, either attached to the mucosal epithelial cells or swimming in the intestinal fluid, that the parasite feeds and reproduces, and it is here that any protective or therapeutic agents must act. Current methods of treatment include the use of metronidazole or quinacrine, but both drugs have unpleasant side effects, and neither is 100% effective (Wolfe, supra).
Bacillus thuringensis (B.t.) with its growing list of subspecies, is known to produce a variety of crystalline protein inclusions that have insecticidal (Gaertner, F. H. [1990] Controlled Delivery of Crop Protection Agents, R. M. Wilkins, Ed., Taylor and Francis, PA, pp. 245-247) or nematicidal activities. The constituent biotoxins of the inclusions, known as .delta.-endotoxins, are highly specific in their activity, affecting only target insects or nematodes. The .delta.-endotoxins described to date (Hofte; H., H. R. Whitely [1989] Microbiol. Rev. 53:242-255) are non-toxic to higher animals, including humans.